1. Field of the Invention:
The invention relates to DC to DC voltage converters and particularly to those in which an amplifier in the primary circuit is driven by autotransformer action in a portion of a transformer primary winding to produce self-oscillation.
2. Description of the Prior Art:
For a low to high voltage conversion it is common to build up current in a transformer winding to a maximum and then interrupt it suddenly so that the magnetic flux field collapses abruptly across the secondary winding to produce a high voltage pulse in the secondary. One known way of doing this is depicted in FIG. 1 where primary winding 10 of transformer 11 has tap 12 for dividing it into main portion 14 and auxiliary portion 15. Transistor 16 has its emitter-base circuit connected in series with portion 15. The emitter-collector circuit of transistor 16 is connected in a series loop with portion 14 and source 17. Start-up bias is provided by resistor 18 from the base of transistor 16 to the negative side of source 17. When switch 20 in series with source 17 is closed, transistor 16 starts conducting providing current through portion 14 and effectively isolating portion 15 from source 17. Autotransformer action between portions 14 and 15 then increases the drive to the base of transistor 16 producing a rapid turn-on of transistor 16 into saturation. As transistor 16 reaches saturation the current in portion 14 begins to stabilize reducing the autotransformer drive to the base of transistor 16 which then starts to turn off. Again autotransformer reaction due to current drop in portion 14 occurs. This time the drive to the base of transistor 16 is reversed turning transistor 16 off in opposition to the bias from resistor 18. Upon stabilization, the bias from resistor 18 starts the cycle anew so that the circuit is free running. The turn-off of transistor 16 is sufficiently abrupt to dump most of the energy stored in core material 21 into secondary winding 22. To the extent the turn-off is not square, there is a loss of efficiency.